Polarity, trigger, & bias scheme

This will be uncharacteristically concise as my new job + domestic duties = dead-tired Prof. Gomez.

So! It occurred to me I hadn't posted how the switch was to be biased, triggered, etc. here it is, hopefully you can make it out:



Note that power dissipation in the biasing resistors can be non-trivial - we'll need high voltage, high value, reasonably precise resistors for this purpose. Naturally none of those I have lying around are even close to the correct values...

good news

My air drier -- which is a necessary component for operating the triggered switch -- is in perfect working order, near as I can tell, aside from the pilot lamp in the power switch being burned out.

Here's a miserable picture of the thing:



It has a little humidity indicator window which contains an "indicating" silica gel, and through which the output air passes, to give a general indication of whether the supplied air is reasonably dry. The silica gel is impregnated with cobalt chloride (which by the way is both a heavy metal poison AND a carcinogen, so treat with enormous respect) which is all-blue at humidity levels below 5% RH. Unfortunately, that corresponds to a dew point of only about -2ºF. The clay zeolite itself is capable of delivering dew points as low as -20ºF. Since we want our air to be as dry as reasonably practicable, this calls for a down stream air drier of silica gel, which will get us down to -40ºF. Achieving a dew point lower than that would require cryogenic temperatures, or bottled gas. If I used silica gel to do the brute force drying of our lovely unpredictable Colorado air, I would be regenerating it constantly. This two-stage setup with the first stage being self-regenerating strikes me as a pretty good way to get relatively free ultra-dry gas, considering I arrived at the hard part on the cheap. I picked up the air drier at an amateur radio swap meet for, I think, $20 USD.

Now then, the humidity indicator was fine the last time I mucked about with the thing, indicating the supply of dry(ish) air. But when I hauled it out again a few years later (last month) it showed all orange and pink for the first hour after I ran it. Oh dear.

According to the preventive maintenance manual I found floating on the internet, when this happens, the zeolite has become saturated and must be replaced. And oh by the way, attempting to service the drying towers in the field voids the warranty, no user serviceable parts inside, refer servicing to qualified service personnel (ie; factory) and blahblahblah.

Now it's been my (admittedly limited) experience that zeolites can be regenerated (ie, their absorbed molecules desorbed) by heating or application of high vacuum or both. In fact, this is done all the time as a matter of course. There are vacuum pumps that work via the principle. Well and so. Simply running the unit wasn't solving the problem, and the unit was supposed to be self-regenerating.

The PM manual mentioned that the towers would not be properly regenerated if the units "short cycled" (the unit turning on and off too often) or if it was operated at a pressure it outside the range it was designed for. Aha. The last time I'd been using it, I had been trying to get it to run continuously, cycling between the two towers as designed, but delivering dry air at a low pressure and flow. I'd been fiddling about with the pressure regulator (which is used in a strange way in this design) and the compressor cutoff switch. I'd managed to get the operating interval and pressure so far out of whack that the towers weren't getting completely regenerated, resulting in a slow build-up of water vapor.

Once I understood better how the thing needs to operate, I was able to set the regulator and the compressor cutoff switch such that the towers were regenerated (assisted by a heat lamp) in just a few hours.

I still need a downstream silica gel drying cartridge to get the final dew point down in the -30 or -40F range, which I'll either pick up on eBay (I'm not liking the prices I'm finding for new ones) or I'll fabricate, since it looks easy and the bulk agent is cheap.

Dew point monitors/sensors for process gas streams exist, but BOY HOWDY are they expensive. With one, the silica gel cartridge might or might not be necessary. With a (far less expensive) silica gel cartridge, the dew point monitor isn't necessary.

The gas system will probably look something like this:


...except that I can already see that I need a small accumulator and a one-way valve between the air drier and the rest of the system. Its output pressure fluctuates too much as is. It's intended to work into a big reservoir, ie; waveguides.

I'm still figuring this out, because I'm trying to make use of as much on-hand parts as possible. I seem to have nearly everything (certainly the big expensive things, like the vacuum pump) but I'm still short a few odds and ends. I need to be able to control pressure very accurately and repeatably, so a capacitance manometer (Baratron) is probably on the shopping list. I've got thermocouple gauge tubes around, but they aren't useful at higher pressures. The Baratron will cover from above atmosphere to 1x10^-3 with almost single-Torr precision. (absolute accuracy I care less about than I do precision for this application, assuming the repeatability is there)

The idea is to only pull fresh dry air (or other working gas mix) through the switch when purging it after a shot. We don't want flowing gas during a shot, as it may introduce instabilities we don't want. It would almost certainly affect jitter although I don't happen to care about that yet. Yet.

So that's what the purge valve is for. We open that after a shot. Then close it and pull the switch down to operating pressure. Depending on how hard it turns out to be to maintain the switch at a constant pressure, I might either add some valves to isolate the switch completely, or I might be forced to bleed a small amount of gas through it all the time to maintain the (very low) pressure, in which case I'll plumb the purge valve around a needle valve upstream of the switch.

Speaking of the switch, here's another really excellent phonecam pic of same, attempting to reveal the geometry or relative position of the trigger plane electrode and the adjacent main electrode:



If I had been paying attention when I took this photo, two o-rings in the insulator portion, which are uncompressed, would have been removed, allowing everything to sit as it would when compressed, and the two electrodes would look about .040 closer than they do. But you get the idea.

Now, I haven't yet got a way to model fields, but based on what I've seen in many papers which depict calculated fields through switches, and the few which lead me to think this design with these shapes of electrodes could work -- based on all that I say, I think the adjacent electrode needs to be a hell of a lot more adjacent. Which is to say, I want the round bit to be closer to the plane of the trigger electrode, but still not protruding through the hole.

Right now, when the switch is fully assembled, the main electrodes are separated by .978". The trigger plane opening is 1.017". We want the hole larger than the main electrode spacing, but that's cutting it a bit finely. I think I may -- eventually -- cut new insulator housing pieces from acrylic, with shorter dimensions. I may only have to replace one piece actually. The one which is the short side now looks about right for the new long side, and a new piece cut from acrylic will be the new short side. I only used this horribly yellow bubbly urethane crap because I had it lying around and it was already exactly the the right ID and OD. It would have made better rollers for some mechanical application...

Anyway, shorter spacing is okay only up to a point. I can't let the main electrode separation (the 'D' in the Paschen Pressure-Distance curve) get too low or my operating pressure will be impractically high and pseudochannel operation may not be possible. And since I originally figured all of this out based around one case: the main electrodes I had on hand (specifically, their radius and height) and the right spacing for operating at 10kV in the pseudospark pressure regime... I should probably figure out the limits before I waste time machining new housing bits.

But as it is, I do not believe the field will distort far enough fast enough (through the trigger hole) to ensure not involving the trigger electrode, not to mention achieve the fast current rise time and commutation time I am hoping for. Besides, shorter is lower inductance. There's a reason many commercial switches look the way they do. And there's a reason my switch resembles a scaled down version of the classic T-508 switch originally developed by Physics International and now sold by Titan Pulsed Systems Division of L-3. Yes, this thing is long and huge (tho half the size of a T-508) but if the circuit geometry is right, that will be an advantage, not a disadvantage. If I'd started any smaller I'd have driven myself mad, not to mention would have had to fabricate more parts from scratch.

Having said all that, I think I will give this thing a shot or three as it is before I rebuild the housing. Parts for the gas circuit and some minor tooling to help me get the holes drilled in the end caps. MAYBE, possibly, even using the drill press, which means much sooner rather than waiting until the mill is up again - no promises on that however. It remains to be seen how clever I can be. I'd rather do good work slowly than sloppy work quickly, so if I think I really need the mill to do this without ruining my pretty end caps (which I would be REALLY upset over if I had to make them again) then it'll just have to wait until I get a phase converter. It's mainly an issue of stability and stiffness and whether the rotary table will fit on the drill press table, and how exactly I'm going to mount my end cap fixture tool to the rotary...

This work was supported by the Joss Research Institute.

Step 1 of {mumble} complete!

As you can hopefully see from the no-doubt indistinct phone-cam shot accompanying this post, the reconfiguration of the trigger electrode is complete.


Next step is to add the extra holes to the switch end-caps that I mentioned in my previous post. To do that, I need to be able to mount the lathe mount I made for the switch end caps into the mill vise. And to do that, I need a big pair of vee blocks than the pair I have. Right then, one more item added to the shopping list. Oi. Been meaning to get a pair for a very long time. I scored a small precision pair on eBay some time ago, but they are too small for this job.

After the mods to the switch are complete, I have to focus on getting the gas handling system and some kind of very fast trigger ready.

For the gas handling part, I have an air drier the media of which needs drying out, a vacuum system which lacks a precision manometer, and so on - about 3/4 of what I need is ready to go or can be. My vacuum system is technically down, but I only need the roughing pump, there's an additional port for that.


As for triggering this thing in field distortion mode, I do not believe the EG&G TM-12 which I have on hand, or indeed any trigger source EG&G made -commercially- is fast enough (gasp! Yes, I said it, tho I'll be delighted to be proved wrong, it just wasn't their usual bailiwick) to multichannel this sucker without going trigatron on me. Trigatron operation means a spark develops between the adjacent electrode and the trigger electrode, and that spark provides the ionization which fires the gap. Some switches are designed to work that way. Unfortunately, in this switch it would probably result in very bad erosion of the trigger electrode, so it's an operating mode to be avoided. I also don't believe that the Pacific-Atlantic Vector Inversion Generator (trigger pulser) is in working condition, although I haven't nailed that status down with certainty yet. I have another miniature VIG in a trigger panel for a Pulsatron I scored from eBay, but I don't know yet whether I can get that unit working either. There are one or two other options, and of course there is always the Marx, except that I think its output might be too high. I know, right? There are worse problems to have. OTOH, it isn't built yet.

Odds are good that I'll try running the switch with just the TM-12 for a trigger, at least once, because I'm dying to run the thing at all. Hopefully running it at relatively low power levels will keep electrode erosion down. The first test shots will be done with a 100Ω load at 10kV, resulting in 1MW dissipated in the load resistor.

And one way or another, I have to get the Bridgeport some 3-ph power again because so many parts and features I need to make require a mill. I am looking at a rotary phase converter from American Rotary, most likely. I'm done mucking about with inverter VFDs, I think. And if any reader is wondering why one doesn't simply swap the motor for a single-phase version, there are various very good reasons which I have arrived at through my own homework and which I feel certain the reader will find far more convincing if she arrives at them himself.

I think I shall shop for a capacitance manometer (Baratron, MKS Instruments) and a simple display for same (Duniway's TeraNova displays are nice) on eBay. I'll need to be able to read the gas pressure in the switch accurately and repeatably. It will take time to find what I need for a price I'm willing to pay, so I'd best start searching now.

This work was supported by The Joss Research Institute, Laurel, MD, USA.

why so serious?

For some time now, and as previously reported, I have been unable to make much headway on any of my Mad Science projects. There are various reasons for this, some good, some not-so-good.

Here are some good ones:

* I've been unemployed since May, and every single project needs parts which must be purchased. Many of said parts are relatively inexpensive, but there has been NO disposable income until recently, and that due solely to the generosity of friends. More on this down below.

* my wife just went through total hip replacement surgery. If you're not familiar with that, please take my word for it that it is brutal and very challenging to recover from. This will be the third such surgery she has endured. Recover takes months, happens at home, and I am all of the nursing staff (poor girl).

* I've got health issues of my own which are severely hampering my ability to do what I'd like to be doing. I'll spare you the details.

And now the good news: I start a new job in January and should have paychecks coming in mid-month.

I've also been honored to receive an honorarium / stipend / fellowship from The Joss Research Institute, a private R&D firm in Maryland. It came with some funds which for now went into paying bills, but which will be pulled back out of my future paychecks and earmarked exclusively for expenditure on my science projects. I think it is entirely appropriate that said money be used exclusively for that, especially given the spirit in which it was given, which was to help remove obstacles to my getting shit done. It's also easy to do this since our credit union gives us several free accounts to stick money into for various purposes.

I have to say, I am quite flattered given the smarts of the guys who gave it to me. We all communicate with several other folks with similar and branching interests along the lines of pulsed power, high voltage, high vacuum, physics experiments, lasers,

To make this post a little better than a place-holder, I offer the following:

My Triggered Spark Gap Switch requires some rework before I strap it to one of the 3kJ pulse caps and a pulse resistor and transfer a 1 kA / 1MW pulse through it.

It turns out I can do at least part of said re-work without spending money. I just need to get a different project off of the lathe so I can work on the trigger plane electrode. Two things need doing:

Thing One
I'll be making the ID about twice as large, all the better to pass a large diffuse plasma discharge, my dear, preferably without actually involving the trigger electrode - remember, this is a field-distortion switch, we hope)

-and-

Thing Two
I'll be removing the radius on the ID, leaving instead an acute angle with a sharp edge. This angle will be tapered on the large-gap side and in-plane on the small-gap side. The better to distort the field with, my dear. However, a sharp-edged trigger plane must be PREZACKLY biased with respect to the ratio of the two gap distances. I have the vague recollection that the ratio of diameter to main electrode distance was to be in the range of 1.0 - 1.6, but my memory is notoriously unreliable, so we'll just leave that a hypothetical until I find the collection of photons and spins states that constitutes a "white paper" these days...

Looky here:

That brass disk with the hole in it, bottom-center, is the trigger plane electrode. The hole in the middle needs to be about twice as big or a bit bigger. Someone mentioned (in some switch white paper I have somewhere) an empirically-arrived-at rule of thumb for main electrode distance vs. hole size for this style of switch, but finding it again will take some time...

As is probably obvious, this switch has not had a single shot through it. I realized after I finished it that the changes were needed. Just now got around to diddling with it in between thirteen other things.

I lied unintentionally: THREE things need doing. A second set of holes in each switch end plate needs to be made, identical to the ones that are there now, but countersunk in the opposite direction, for bolting the switch into a transmission line or to coaxial test loads. Having a bolt circle lets me fashion large-diameter connections and current paths which translate in the general case to low distributed inductance, which informs the minimum attainable pulse rise time. Readers who have read my earlier descriptive material here and on Flickr will have gleaned that a big part of what I am hoping to do with this switch is not merely transfer big lumps of energy around, but to achieve very fast switching speeds and commutation times -- fast, that is, for a rank amateur with not formal schooling in pulsed power!

Oh yes, I will be studying calculus in 2012, or that's the plan anyway.

I'm just not in any shape to finish the project currently occupying the lathe and which I don't want to re-center later. Humph. But I am not idle. I'll get some of the above done soonish I think. Things ought to be a LOT better in 2012 than they have in a very long time.

Stay tuned.

even yet more further additional progress on my "Last Tesla Coil", book two, part twelve, chapter 27...

You might think this is the nearly-finished primary of a Tesla coil. And you would be reasonable to think so. But you would be mistaken. This is a laceration engine.

Well, I couldn't wear gloves because I needed the dexterity and the clearance between turns. I tried. I tried rubber gloves, but they didn't protect, just as I'd expected.

After I get done putting Band-Aids™ on all my fingertips, I'll have one more go at straightening and evening-up the turns, leaving them a bit tighter (to keep them from shifting -- as much), which is to say less of a perfect spiral, and more of an octagon. Then I will cut the outer end to its final length and screw it down. Wee! All this should be done a few hours after this post goes up.

It will be badly tempting to lash up a primary circuit for it just so I can try it out, but although I have most of the parts, nothing is put together. Also, I don't have quite enough capacitance, methinks. Gotta go through the calcs one more time after I measure the as-built primary inductance and plug it into the formulae. Furthermore, the HV transformer for this coil is practically unreplaceable, and I'll be damned if I will blow it up, which means I really need to finish the "Terry Filter" for it before running it. *sigh* Did I ever mention this? This coil will be fed by DC, so no resonant charging. I wish to be very kind to my precious 120mA NST, and I am effectively isolating it from the primary circuit entirely.


I wish there was a way to make that primary stay this pretty pink color forever, but there isn't. If I spray it with acrylic now, the acrylic will get all over the finished wood and mess up its finish. It wasn't practical to spray it before installing it - I thought about it for all of ten seconds. There's over 90 feet of 1" copper strip here, so I'm not gonna be dabbing Futura on it with a cotton swab, or laying it out on the sidewalk to spray it.

I'll spray or coat (Futura floor wax also works great) all the brass. That'll have to be enough shiny. The copper will all be dull brown in ten years.

I'll take a "glamor shot" of the complete Tesla coil primary and secondary -- minus one minor dodge I have to add to the strike rail -- later tonight.

Okay, it's later:


Inquiring minds will want to know what else needs to be finished before it runs. Here's a laundry list:

* primary capacitor - this will be an MMC of course, the most reliable sort there is. I have most of the caps for this, bought as a "finished" (bleh) MMC, but I am not comfortable with the number of caps in each string (determines the maximum safe operating voltage of the complete array) so I will need to add a cap or two to each string. Since that lowers the capacitance of each string I'll need to buy enough additional caps to add another string or two as well. The cap will be built with brass "strapping" terminals mounted on the exterior so that any number of strings may be placed in or out of circuit.

* spark gaps - I have one spark gap completed, but intend to build at least two more. The finished one is the "sucker gap" previously about posted here. I've got a disk, hub, and shaft done for an asynchronous rotary. I've got all the electrodes made, but not yet drilled, for a Richard Quick style gap. I've made nothing else nor thought about the housing for that. I'd kinda like to make a gap like one that Old Nik' was known to have used in his original NYC lab before it burned to the ground. It was just a bunch of brass balls in series. Not the best performing gap, but if memory serves, that was long before he'd invented several new kinds of fast-quenching gap switches.

* control panel - again, I've got most of the expensive parts for this, but there's a lot of finicky work to be done on said parts. I'll need to make new cards for the meters. I'll need to obtain a few specialty parts like a current transformer. The HV transformer is HEAVY so I'm considering building a cart for the control panel rack cabinet (which will be heavy enough without the transformer in it) and possibly putting the transformer in the cart/base. I might leave it in the panel cabinet and use the cart/base for storage of cables and parts. I haven't thought very much about that. And there's surely a ton of small parts I don't have, like controls. Much work to be done there.

* the damned primary tap connectors. These are gonna be finicky to make, but a joy to have and use versus any other primary tap method I've ever seen used by anyone, anywhere. So there. Okay look, that crazy rotating thing with the sliding brushes doesn't count - that's not "tapping". Yeah. So anyway, I think I've got the design worked out. I haven't started collecting various red metals (copper, brass, bronze) yet. And I have to make two of them. Bleh.

* cabling & miscellanea - the ground connections, a ground rod kit with straps, the umbilical between control panel and coil, to name a few examples.

So there is still a long, long way to go before we see first light on this beast.

PS: I noticed just now that pictures in some of my older posts are missing. I'll look into this in a bit. Probably nobody but me noticed anyway.

more progress on "My Last Tesla Coil"

Here is a sight a few of my friends thought they would never see. The primary deck and all of the primary supports are finally complete. It may not look like much, but it's been a great deal of hand-sawing and sanding to get to this point.

This was also the day I I cut the two pieces of the strike ring and installed them. Those bits - including the strike ring insulators - will come off before I varnish the primary supports.


I have a bit of sanding to do on one or two primary supports before I start varnishing, but they are essentially done and they are installed semi-permanently. I refrained from using glue on them in case one gets broken off at some date in the distant future. With only screws holding them on, it will at least be possible to repair them.

I should have the varnishing of the primary supports done in a week, at which point I will start installing the primary copper. I will probably give them either a clear coat (depending how it looks on a test) or a very light stain and urethane, because these supports are hard rock maple and have a beautiful grain.

Oh by the way, the ground connection to the strike ring is already made, at least as far as the primary deck ground connection that exists so far... can you guess where and how?

PS: oh, and yes, that strike ring constitutes a shorted turn, an undesirable thing. I remember thinking a long time ago that I should do something about that when I got around to cutting it to fit and installing it. And now that I've done that, I still can't decide what to do about the shorted turn issue, because everything I've thought of so far seems ugly. I will probably conceal a break within an insulated sleeve concealed inside a slightly oversized mounting tab.

Tesla coil primary deck progress

Due to being unemployed for three months and my arthritis acting up badly, I've been largely ignoring hobby projects lately. I've always got an excuse. But today I finished cutting and routing the slots in the primary deck.

The slots are for access to the primary windings from below. One of the things that has always bothered me about most Tesla coils (including mine) was that the adjustable primary tap connection was nearly always brought out from below the primary deck around the edge and over the top. This had two effects: it wasted inductance in the primary circuit (ie; stray inductance which does not contribute to the magnetic field of the primary) and it created a convenient high spot from which corona leaders could start - a place for the secondary streamers to strike.

I have a little cleaning up to do, then I'll touch up the varnish in the slots, do some more finishing work on the bottom, and then mount the primary supports, and finally re-coat the whole top deck.

More as it happens. Stay tuned...

quickie

 Couldn't sleep, so I updated my proposed design for the EML (pssst: "rale guhn" don't tell anyone) projectile package.  I added a keyway to hopefully keep armature and cap wedded at least until they exit.  Yes, discarding sabots are nice, but let's get the thing working at all first, shall we?

The lighter, white-ish cap on the right is to be made of Delrin (acetyl).  The armature proper at rear is made of high-conductivity aluminum, 1100 series or the like.  I may be able to find this profile off-the-shelf, saving me a lot of machining.  The gaps creating individual fingers are just saw kerfs.  The key and keyway will be done with a dovetail mill.

I might see if I can talk my friend with the CNC mill to set up and knock out about 100 pieces of each.

Note that the size is not pinned down yet.  The design currently calls for a .75" bore.  If I am to use the rails I have in hand, that will be the case.  If I can get my hands on some bigger rails (at the price of copper today? Hah!) I would like to have more inductance in the launcher, just to increase the ratio of stray inductance (wasted) and launcher inductance (creates force on the armature).

 The fingers are a dodge that's been tried a few times by several labs and which seem promising for square bores having very little pre-load on the armature. At the small scales amateur launchers are working at, and tens of kilojoules input energy, we can't afford to waste much of that energy overcoming stiction from a pressed-in armature.  Conversely, since we're in the kilo-amp regime, we don't have as much difficulty with sliding contact resistance as the bigger devices do.  Some preloading will absolutely be necessary, but I want to keep it to a minimum.

Fortunately, this launcher has a very high pressure pre-accelerator, compared to most amateur-built devices.

PS: the shape of the void behind the armature -- or, if you prefer, the inside shape of the contact fingers -- would be better if the fingers were thicker toward the armature than shown here, but the armature proper was designed with off-the-shelf c-channel stock in mind to save time and money.

Tesla coil progress

Due to lack of employment and therefore money (and other reasons I won't get into) the various projects I had been actively working on have ground to a halt, so I turned back to what I'd been pushing before I got distracted by the Mad Scientist Light Switch, Fast Compact Marx Generator, and the Field-Distortion-Triggered Spark Gap Switch: my "Last Tesla Coil".

It was tabled because I lacked the copper strip (about 10 pounds worth) for the primary and the money to buy same.  I got lucky and scored (more or less) what I wanted while working on the aforementioned stuff so with that in hand, and certain other difficulties being somewhat ameliorated, I can resume work on it.

So, this post is about the primary coil, its support structure or "deck" as I call it, a grounded "strike rail" mounted above and to the outside of the primary winding, and the various bits and bobs to make it all work.

I'm building this thing with several goals in mind which I don't often see implemented in other Tesla coils, even those built professionally for museums.  I want it to have a classic, slightly ornamental, but thoroughly old-world hand-made. I want the build quality to be top notch.  I'd like to see it last at least as long as the Griffith Park Observatory coil lasted before some future coiler has to rebuild it.  I'd like to see it find its way into a museum or educational facility, so it needs to be well made and sturdy.  Unfortunately, I also want it to be portable, so it can't be as sturdy as it would be if it was never to be  moved.  I want it to have the highest possible performance while retaining spark gap operation.  Honest to goodness, for long term reliability and simple lifetime I believe an old-fashioned spark gap coil will last longer than a more efficient and higher-performing solid state coil.

So, for ease of use, the primary will be accessible (for tap connections, using a special connector I've designed) from below the primary deck through any one of eight radial slots.  These slots would significantly weaken the deck structurally if it were not for the primary supports which stiffen the deck radially and a glue-lam reinforcing rib around the circumference of the deck.

Here's the glue-lam rib being glued and screwed to the underside of the deck:

 The sanded areas on the bottom will be finished with urethane stain/varnish just like the top, after everything that needs gluing is done.  Holes for the ends of the radial slots have been drilled, but the slots have not yet been cut out. The black objects are ABS sockets for the uprights which support the primary deck above the base.  This "post and two decks" implementation is a very common construction style for amateur-built Tesla coils.  It's not as nice looking as a full box or base (of any shape) but it's a lot lighter, it knocks down, and is therefore MUCH more portable.  That ring was finished two years ago, and the deck was ready before that.  Because of how this thing goes together, it is necessary that construction of the primary deck go in a specific order of steps.  I couldn't glue this on until various other things happened, culminating in the need for the copper.  Once I obtained the necessary copper, I was able to answer various questions letting me finally finish this bit.

The next bits necessary for this thing are the primary supports, which were last seen looking like THIS.

This week, I finished all of the brass "P-clips" which will fasten the strike rail to the strike rail insulators which are those white cylinders with the button-head cap screws in the ends.  Now they look like this:

The clips are all done.  Each was individually hand made from brass strip because I couldn't find what I wanted off the shelf.

The supports (which by the way are maple and are going to be f_cking gorgeous when they are stained and finished) have been marked with pencil for the saw cuts which will hold the primary windings. Each support has its cuts offset from those of its neighbors by 1/8 of the distance between two cuts, so that the spiral of the primary will be as smooth and step-free as possible.  That is solely an issue of aesthetics, it will not affect performance.  The long piece is a special feed-through for the ground connection to the strike rail on support #1.  This connection passes entirely through the primary support and deck, is insulated to prevent primary voltage from reaching it (and setting its primary support on fire) and connected to the secondary's bottom ground connection through a brass strap attached to the bottom of the primary deck.

Now comes the "fun" part, and by "fun" I of course mean painful, torturous labor:

 Each of the eight primary supports must receive fifteen carefully spaced saw cuts, for a total of 120.  Maple is HARD even among hardwoods.  As you can see, I have already damaged the tops in a few places.  That's what happens when you're exhausted, with aching, twitchy muscles, and you decide to press onward anyway. *sigh*
I have arthritis and other musculoskeletal maladies, so this part is going to go very slowly, but just like those thrice-damned brass clips, if I do a little each day, in a week I'll be done. This is all being done by hand, as I do not own much in the way of wood working power tools, and in any case, this would require a very special (thin) power saw blade indeed, of a sort I've never seen.  I am using a "back saw" (normally used in a miter box) to make cuts roughly the same width of the copper's thickness, so I shouldn't need anything fancy to keep the windings from shifting in their supports.

More as it happens, stay tuned.

more delays and worse

 Due to a long spate of misfortune and a short run of stupidity, I will be unable to work on any of my projects, nor have time to write about them, for at least another month, perhaps longer.

I'll resume when I resume.

And no, I am not incarcerated.  At least, not yet.